Control units for hydraulic rams



Apnl 18, 1961 H. NORTON ET AL CONTROL UNITS FOR HYDRAULIC RAMS Filed Sept. 25, 1959 QNVENTQRS HENRY NORTON HERBERT V- NORTON LESLIE. B. NORTON DouaLAs E. NORTON sR'rTo RN EYS Unite States atet ham Norton, and Douglas Edwin Norton, all of Harley,

England, assignors to Norton Tool Company Limited, Horley, England, a company of Great Britain Filed Sept. 25,1959, Ser. No. 842,311 Claims priority, application Great Britain Oct. 1, 1958 5 Claims. (Cl. 121-38) This invention relates'to control units for hydraulic rams suitable for numerous applications, for instance, for actuating machine tools such as hydraulic presses, shapers and slotters, power transmission systems, mechanical handling equipment and rock drills.

The control unit of the invention is applicable more particularly, but not exclusively, to the hydraulic ram apparatus described in the present applicants co-pending patent application No. 842,509 filed concurrently here'- with.

It is an object of the invention to provide a single control unit by which the ram can be caused to perform a wide range of operations.

According to the present invention a control unit for a hydraulic ram comprises an unloader valve communieating with the pressure chamber of the ram (i.e. the chamber to which pressure fluid is introduced to produce the working stroke) and arranged to open and vent the pressure chamber when a predetermined high pressure is attained, and to be held open, until released, by substantially lower pressure, and a release valve which can be opened to permit closure of the unloader valve.

The unloader valve may comprise a cylinder containing a spring-loaded piston of relatively large area controlling a port in the cylinder wall and carrying a closure member which can seat on a seating of much smaller area than the piston and communicating with the pressure chamber of the ram, such that the closure member is lifted from its seating by the said predetermined high pressure and a space on the closure member side of the piston thereupon communicates with the said pressure chamber, the port being disposed so that fluid is trapped in this space to prevent complete closure of the valve until the trapped fluid is released from this space.

The unloader valve of the control unit acts as a means for stopping the working stroke and initiating the return stroke automatically.

Opening the release valve after the end of the return stroke, or even before completion of this stroke, will permit the unloader valve to close and so start a new working stroke. By delaying the actuation of the release valve any desired dwell at the end of the return stroke can be achieved. The release valve therefore constitutes a single control giving single working strokes followed by an automatic return stroke of controllable length and with a controllable dwell before the next working stroke.

If desired the loading of the unloader valve spring may be adjustable so that the predetermined high pressure at which the unloader valve opens and hence the maximum working force exerted by the ram can be varied as required.

A further extension of the effects achievable by the control unit is provided if an adjustable bleed valve is connected in parallel with the release valve. The bleed valve permits leakage of fluid trapped in the space in the unloader valve at a controlled rate and therefore permits the unloader valve to close automatically after a controllable delay. This provides automatic multi-strokeop- 'ice eration with a controllable dwell at the end of the return stroke. The bleed valve can also provide for a series of short strokes in rapid succession, the length and the frequency of the strokes being variable by adjusting the bleed valve.

The control unit may also include a separately actuated control valve communicating with the pressure chamber of the ram and operable to control release of pressure from this chamber independently of the unloader valve of the control unit. By opening the control valve a working stroke can be terminated and a return stroke begun, the return stroke continuing until the ram comes up against a return dead-stop or until the control valve is re-closed. The control valve therefore provides control over the length of individual strokes. If the control valve is sensitive to the force applied to its actuating member it can also provide control over the fluid pressure in the pressure chamber of the ram and hence over the working force exerted by the ram. This device provides control over the actual working force whereas an unloader valve of the control unit having an adjustable spring provides control only of the maximum working force.

Preferably the invention is applied to a hydraulic ram control system in which the underside of the ram piston is under pressure at all times, since in such a system ram reversal is achieved virtually instantaneously in response to actuation of the unloader valve on the separately actuated control valve, permitting very rapid multi-stroke operation.

The invention may be performed in various ways, and one specific embodiment will now be described by way of example with reference to the accompanying drawing, which is a diagrammatic representation of one form of control unit embodying the invention applied to hydraulic ram apparatus as described in the aforementioned copending application.

It is to be understood that the control unit and the hydraulic ram apparatus are depicted in a highly diagrammatic form, with the object of illustrating the principles of the invention and the way the various parts of the control unit operate rather than the details of design and construction.

Referring to the drawing, the hydraulic ram apparatus comprises a double-acting hydraulic ram 10, depicted in this case as applied to a hydraulic press. The pressure chamber 11 and the return chamber 12 of the ram are connected together by a connecting passage 13 which includes a restrictor valve 14, preferably an automatic unloader valve as described in the said co-pending application. On the return chamber side of the valve 14 the connecting passage 1'3 is supplied with hydraulic fluid from a high pressure pump 15. To provide afast approach portion of the working stroke of the ram there is a low pressure pump 16 which can deliver fluid to the pressure chamber 11 through a non-return valve 17. A relief valve 18 is provided for venting the low pressure pump to a return line 19 when the non-return valve 17 is closed. Also communicating with the pressure chamber 11 through a line 20 is a control unit 21. This has an inlet chamber 22 with which the line 20 is in permanent communication and a return chamber 23 which is in permanent communication with the return line 19. Communicating with the inlet chamber 21 is a passage 24 equipped with a control valve 25. When this valve is open, fluid can flow out from the pressure chamber 11 through the line 20, the inlet passage 22, the passage 24 and the control valve 25 into the return passage 23, and then out through the return line 19. The control valve 25 is actuated directly by an actuating member 26, through a rod 27. Thus the fluid pressure at which it will open is a function of the force applied to the actuating pressure supply to the pressure chamber 11 to maintain the fluid pressure on the ram at the desired value, this value being adjustable by pressing more or less heavily on the adjusting member 26. The working stroke can be stopped by raising the adjusting member 26, and a new working stroke begun by lowering it again. The control valve 25 actuated by the adjusting member 26 therefore provides manual control over the individual working and return strokes, and control over the working force of the ram. The control valve 25 corresponds in functioning and effect to the control valve of the apparatus described in the said co-pending application.

The control unit 21 of the present invention, however, also provides additional effects. One such effect is provided by an unloader valve 28. This consists of a cylinder 2% in which can slide a piston 30 which is loaded towards the left in the drawing by a spring 31. The right-hand abutment '32 of this spring is adjustable by an adjustment screw 33. A pin 34 fixed to the piston 30 bears against the head of a valve 35 which when open permits fluid from the inlet chamber 22 to enter a chamber 36. When the valve 35 is closed the pressure in the inlet chamber 22 acts only on the area of the valve, but as soon as the valve 35 begins to open the pressure in the chamber 22 is applied to the whole area of the piston 30, and continues to be applied to that large area so long as the valve 35 remains open. Consequently, the pressure in the inlet chamber 22 required to open the valve 35 is much greater than the pressure at which this valve will close again. Also, when the pressure in the inlet chamber 22 rises high enough to move the valve 35 only a short distance from its seating, the consequent application of this pressure over the large area of the piston 30 will move the piston far enough to the right to expose a port 37 in the wall of the cylinder 29. This port communicates with the return passage 19.

Thus the unloader valve 28 acts as a means for stopping the working stroke of the ram and initiating the return stroke automatically on the attainment of a predetermined high pressure in the pressure chamber 11. When this high pressure is reached, for instance when the ram comes up against a dead-stop at the end of its working stroke, or when it is exerting its maximum working force corresponding to this pressure, the unloader valve 2% will be opened and will vent the pressure chamber 11 to the return line 19, through the line 20, the inlet chamber 22, the valve 35, the chamber 36, the port 37 and the return passage 23. This will permit the pressure in the return chamber 12 to return the ram. The magnitude of the pressure at which the unloader valve 28 opens 'can be adjusted by means of the adjusting screw 33.

At the end of the return stroke of the ram the reduction in flow through the unloader valve 23 will permit the piston '36 to return to the left until the port 37 is just closed. However, the piston 30 cannot move. further to the left because fluid is trapped in the chamber 36. This trapped fluid can be released by opening a release valve 38 which is actuated by an actuating member 39. The released fluid enters the return passage 23 and drains away through the return line 19. Release of the trapped fluid from the chamber 36 permits the piston to move further to the left and close the valve 35. The next working stroke of the ram can now begin. The return stroke can be terminated, if desired, before its completion simply by opening the release valve 38 earlier and so permitting the unloader valve 28 to close and shut off the escape of fluid from theram pressure chamber 11. Thus the release valve 38 provides manual control over the duration of-the dwell or delay period at the end of a anemone completed return stroke, and over the length of the return stroke.

Another way of releasing the trapped fluid from the chamber 36 is through a bleed passage 40 controlled by an adjustable bleed valve 41. -This valve permits the trapped fluid to escape at a controlled rate and therefore'permits the unloader valve 28 to close automatically after an adjustable delay. This provides automatic multi-stroke operation with an adjustable dwell at the end of the return stroke. If the bleed valve 41 is opened more widely it is possible to terminate the return stroke automatically before its normal completion and begin a new working stroke immediately, providing a series of short strokes in rapid succession, the length and frequency of the strokes being variable by adjusting the bleed valve 41.

The various controls and adjustments of the control unit, namely the release valve 38, the unloader spring adjustment 33, the bleed valve 41 and the control valve 25, may be actuated manually as illustrated, or one or more may be actuated automatically depending on the degree of automatic operation required in the particular installation. For instance, the release valve 38 may be actuated automatically by the ram at the end of the return stroke to provide multi-stroke operation. This would enable the bleed valve 41 to be dispensed with, but for many installations the bleed valve is a more flexible way of achieving a similar result. Automatic actuation may also be effected to co-ordinate and synchronise the movements of the ram with other operations performed by the same or different machines. The actual form of the automatic actuating mechanism may vary widely' depending upon the nature of the installation and other factors. For instance, hydraulic, electrical or mechanical actuators and transmission links may be employed.

What we claim as our invention and desire to secure by Letters Patent is:

l. A control unit for a hydraulic ram having a pressure chamber, said control unit comprising an unloader valve, a release valve, said unloader valve comprising a cylinder having a side wall provided with a port and end walls, a piston of relatively large area slidable in said cylinder and controlling said port, an inlet connection to said cylinder in one of said end walls thereof, a seating adjacent said inlet connection of relatively small area, an inlet closure member carried by said piston and seatable on said seating, passage means connecting said inlet connection to said pressure chamber of said ram, a spring acting on said piston and urging said piston towards a closed position in which said closure member engages said seating and said ports is closed, said piston having also an open position in which said closure member is off its seating and said part is exposed, said piston being movable'from said closed position by the attainment of a predetermined high pressure at said inlet connection and being maintainable in said open position by a pressure substantially below said predetermined high pressure, said piston also having an intermediate position in which said port is closed but said closure member is off its seating, said release valve communicating with said cylinder and having an open condition in which it releases fluid from said cylinder to permit said piston to move from its intermediate condition to its closed condition.

2. A control unit according to claim 1, in which said spring has an adjustable abutment whereby the loading of said spring is adjustable.

3. A control unit according to claim 1, which includes an adjustable bleed valve connected in parallel with said release valve to provide controlled slow closure of said unloader valve with said release valve closed.

4. A control unit according to claim 1, which includes a control valve, actuating means for said control valve,

mesons-s and passage means connecting said control valve 'to said pressure chamber of said ram.

5. A control unit according to claim 4, in which said control valve comprises an actuating member adapted for manual operation, a seating, a closure member, and means connecting said actuating member to said closure member whereby a force applied to said actuating member urges said closure member towards its seating with a force which is a function of the force applied to said actuating member.

References Cited in the file of this patent UNITED STATES PATENTS 

